Pack spawning is one of the most important farm mechanics to optmize because if you go from the absolute worst scenario to the best it will increase your farm's rates by 4 times. Mincraft mobs spawn in packs, I don't know why but they do. Packs can spawn with up to 4 mobs in them if every attempt is sucessfull. If a pack spawn hits a block that is in the way of its spawn it will stop all future spawn attempts in that pack. Pack spawns also move up to 5 blocks in bolth directions so the maximum pack spawn distance is 20 blocks. A way we can optimize this is by adding a pack spawning roof. This is just non spawnable blocks in a 20 block in each direction roof around your farm. You can go with less than 20 if you want but you are taking the risk that you loose spawns. If you don't have a pack spawn roof and a mob tries to spawn right outside your farm it will fail and stop all spawn attempts in that pack, but if you do have a roof it will instead fail but go onto the next spawn attempt and if you get lucky the other 3 might be inside your farm.